Segment Information - Net Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Net income	$ 273	$ 630
Dividends declared on preferred stock	5	5
Net income available to common stockholders	268	625
Corporate
Segment Reporting Information [Line Items]
Net income	(91)	0
Property and Casualty, Commercial Insurance [Member]
Segment Reporting Information [Line Items]
Net income	121	363
Property and Casualty, Personal Insurance [Member]
Segment Reporting Information [Line Items]
Net income	98	96
Property & Casualty Other Operations
Segment Reporting Information [Line Items]
Net income	5	23
Group Insurance Policy [Member]
Segment Reporting Information [Line Items]
Net income	104	118
Mutual Fund [Member]
Segment Reporting Information [Line Items]
Net income	$ 36	$ 30